Portable electromagnetic hearing aid



Sept. 12, 1956 w. DEMANT 2,522,099

, "PORTABLE ELECTROMAGNETIC HEARING AID Filed Feb. 26, 1948 IN V EN TOR.Wu. L. m M QEMANT .4 TTORNE X Patented Sept. 12, 1950 s PATENT camsPORTABLE ELEGTROMAGNETIC HEARING AID Willian Demant, Copenhagen, DenmarkApplication-February 26, 1948, Serial No. 10,963 In Denmark December 20,1946 Section 1, Public Law- 690, August 8, 1946 Patent expires December20, 1966 The present invention relates to a. portable, electro-inagnetichearing aid'for bone conduction in which apparatus the armature of the'maghetic system is fastened to the interior wall of a casing,

preferably of non-magnetic material, enclosing the'magnetic system,whereas the said magnetic system is'elastically suspended so that it mayoscillate in relation to the armature. 1

In a known hearing aid of this type, the diaphragm consists of arelatively rigid, thick metal plate which for the purpose of reducingthe rigidity has been slotted both lengthwise and crosswise. Besidesthrough the slots thus formed, the space between the diaphragm andmagnetic system is at the sides connected with the space in the casingsurrounding the magnetic system. On account of the relatively greatrigidity of the diaphragm, the apparatus will have a natural frequencywithin the audible range, and by the said arrangement of the apparatusthe air space between the diaphragm and the magnetic system cannot serveto dampen these natural, Y oscillations.

These disadvantages are overcome by the hearing aid according to theinvention, in that the magnetic system is fastened to the bottom of abowl-shaped casing across which a relatively invention the advantage isderived that the bowlshaped casing along its edge is provided withthreads to which a nut carrying the diaphragm is screwed. This entailsthe advantage that a readjustment of the distance between the diaphragmand the poles of the magnetic system may very easily be undertakenwithout the use of special tools.

In the following the invention is explained in detail and describedunder reference to the drawing showing an embodiment of the invention.

The hearing aid according to the invention consists on the outside of acasing composed of two parts, namely a plate-shaped part I and abow1-shaped part 2. The armature of the mag- .ZJ-Claims. (o1. na -114) v2 netic system is in the form of a flat, circular iron disc 3, throughthe middle of which a hole has been drilled or otherwise made, throughwhich hole a brass bushing. 4 is inserted. The bushing 4 is as shown inthe upper part of the drawing provided with a broad collar 5, betweenwhich and the armature is placed the diaphragm 6, in the middle of whicha hole is provided, and between the diaphragm and the armature a disc Iof, for instance, Pertinax or fibre, is inserted in order to prevent thediaphragm from ringing against the armature.

The part of the bushing shown in the lower part of the drawing is beadedaround the edge of the hole in the centre of the armature, so that thediaphragm 6%, will be firmly secured between the collar 5 and the disc1.

Around the diaphragm 6 the edge of a nut 8 is flanged. Into this nut isscrewed a bowlshaped casing 9, and the connection is secured by means ofa lock nut 10.

To the bottom of the casing 9, the magnetic system is fastened. Itconsists of a permanent magnet I l with poles l2 of soft iron, aroundwhich windings l3 are placed.

Through the bottom of the casing 9 fine canals have been drilled,through which pipes Id of insulating material are inserted. Throughthese pipes the ends of the magnet windings 13 are taken to solderingwebs I5. The pipes M fit tightly into the canals in the bottom of theeasing, so that the air may pass from the interior of the casing to thesurrounding spaces only through these very thin pipes, the cross-sectionarea of which is further reduced by the wires to the magnet windings.The pipes may, further be entirely closed, e. g. by means of a coatingof lac.

As will be understood, there will thus be no possibility or only veryslight possibility for the air inside the casing to be caused to flow inand out by the movements of the diaphragm 6. This means that the airinside the casing 9 will act as a dampening cushion during theoscillations of the diaphragm 6. This will entail the advantage that thoscillations of the magnetic system and the casing 9, while theapparatus is in use, will only to a Very slight extent develop intonatural oscillations, and when furthermore, the diaphragm 6 is of verythin material while the mass of the magnetic system and the casing 9 isrelatively great, it will be understood that the apparatus according tothe invention will be able to reproduce sound with exceedingly greatpurity of tone.

Having now described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. A portable electromagnetic hearing aid for bone conduction,comprising an outer casing, an armature member and a resilientsound-receiving diaphragm concentrically and fixedly attached to eachother and to the inner wall of said casing, a second bowl-shaped casinginside said first casing being attached along its edge to said diaphragmso as to be supported and substantially air-tightly closed thereby, andan electro-magnet system mounted in said second casing and having polepieces coacting with said armature member, the second bowl-shaped casingand the soundreceiving diaphragm forming a substantially airtightenclosure for said electro-magnet system whereby an air cushion isprovided in said second bowl-shaped casing.

2. A portable electromagnetic hearing aid for bone conduction,comprising an outer casing, a circular resilient sound-receivingdiaphragm at its center fixedly attached to the inner wall of saidcasing in spaced relation therewith, an armature member attached to thecenter of said diaphragm on the side away from said inner wall, athreaded ring member provided with a flange portion engaging thecircumferential rim of said 4 diaphragm, a second bowl-shaped casinginside said first casing and having a threaded portion along its edgeadapted to adjustably engage said threaded ring member, said diaphragmthereby resiliently supporting and substantially air-tightly closingsaid bowl-shaped casing, and an electro-magnet system mounted insidesaid bowlshaped casing and having pole pieces coacting with saidarmature member, the second bowlshaped casing and the sound-receivingdiaphragm forming a substantially air-tight enclosure for saidelectro-magnet system whereby an air cushion is provided in said secondboW1- shaped casing.

WILLIAM DEMANT.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,149,610 Allis Aug. 10, 19151,507,171 Hahneman et al. Sept. 2, 1924 2,086,630 Miner July 13, 19372,127,468 Greibach Aug. 16, 1938 2,169,306 Lain et a1 Aug. 15, 19392,202,906 Hawley June 4, 1940

